An inkjet printer typically includes one or more cartridges that contain ink. In some designs, the cartridge has discrete reservoirs of more than one color of ink. Each reservoir is connected via a conduit to a printhead that is mounted to the body of the cartridge. The reservoir may be carried by the cartridge or mounted in the printer and connected by a flexible conduit to the cartridge. The printhead is controlled for ejecting minute drops of ink from the printhead to a printing medium, such as paper, that is advanced through the printer.
The mechanism for expelling ink drops from each ink chamber (known as a “drop generator”) includes a heat transducer, which typically comprises a thin-film resistor. The resistor is carried on an insulated substrate, such as a silicon die. The resistor material layer is covered with suitable passivation and cavitation-protection layers. The resistor has conductive traces attached thereto so that the resistor can be driven (heated) with pulses of electrical current. The heat from the resistor can form a vapor bubble in each ink chamber. Rapid expansion of the bubble propels an ink drop through the nozzle that is adjacent to the ink chamber.
Many of the components of the drop generators are fabricated or processed in ways that include photoimaging and other etch processing techniques similar to those used in semiconductor device manufacturing. The components are typically incorporated into and carried on a front surface of a rigid silicon substrate. The front surface of the substrate can also be shaped by etching to form a trench in that surface. The trench is later connected with a slot that is cut through the back of the substrate so that liquid ink may flow from the reservoir, through the connected slot and trench, and to the individual drop generators.
The trench that is etched in the substrate surface is located adjacent to the drop generator components. Also, the silicon etching that forms the trenches typically takes place after some or all of the drop generator components have been added to the substrate. Care may be taken when etching the trenches so as to not damage drop generator components. For example, the portion of the silicon substrate that is etched may be carefully defined on the substrate by masking the area to be etched with material that resists the effects of the etchant that is used for etching the trenches in the silicon. Despite efforts to efficiently form the trench and the drop generator components on the substrate, greater efficiencies can lead to additional cost and time savings.